-LRB- CNN -RRB- -- Federal civil rights investigators have found `` reasonable cause '' to believe that police in Portland , Oregon , use `` unnecessary or unreasonable force '' with persons who have mental illness , the U.S. Justice Department said .

The department 's civil rights division and U.S. Attorney 's Office in Oregon issued a letter to Portland Mayor Sam Adams stating that local and federal authorities will `` continue our collaborative relationship to craft sustainable remedies . ''

In the 42-page letter , federal officials outline remedies that include training and new policies to investigate alleged police misconduct .

Investigators found cause to believe that the Portland Police Bureau engages in `` a pattern or practice of using excessive force in encounters involving people with actual or perceived mental illness . ''

`` We found instances that support a pattern of dangerous uses of force against persons who posed little or no threat and who could not , as a result of their mental illness , comply with officers ' commands , '' said the letter , which was signed by Assistant Attorney General Thomas E. Perez and U.S. Attorney Amanda Marshall .

`` We also found that PPB employs practices that escalate the use of force where there were clear earlier junctures when the force could have been avoided or minimized . ''

One incident in December 2010 involved several officers who used `` repeated closed-fist punches and repeated shocking of a subject who was to be placed on a mental health hold , '' the letter said .

Adams , in a posting on his web page , vowed that the city and its Police Bureau would improve quickly , and listed a series of changes :

-- The city will revise its use-of-force policies -- particularly those regarding the use of stun guns -- `` to ensure that officers have necessary guidance when encountering someone with mental illness or perceived to have mental illness . ''

-- The police will expand their Mobile Crisis Unit -- composed of an officer and a mental health worker -- `` to ensure availability at all times and enhance non-law enforcement capacity to respond to persons in crisis that do not pose a public safety threat . ''

-- The city will establish a mental health desk at its 911 calling center to ensure calls are properly dispatched .

-- The city will lead efforts to boost community mental health treatment options , such as establishing a 24-hour secure drop-off and walk-in center , `` that will provide police officers more options when assisting persons experiencing a mental health crisis . ''

-- The city will use an early intervention system to identify officers , supervisors and units `` for non-punitive corrective action , and to assess gaps in policy , training , supervision and accountability . ''

-- The city will move to speed investigations of complaints about possible officer misconduct .

-- A community body composed of representatives of a variety of groups will assess how well the agreement is being implemented , offer recommendations on additional steps , and advise the police chief and Adams on how to improve community relations .

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Civil rights investigators say Portland Police engage in a pattern of excessive force

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Victims are persons who have or are perceived to have mental illness

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Portland mayor vows to institute changes -- quickly